25. Sistematica Campbell

8/4/2019 25. Sistematica Campbell

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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBiology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 25

Phylogeny and Systematics


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Overview: Investigating the Tree of Life

Phylogeny is the evolutionary history of a speciesor group of related species

Biologists draw on the fossil record, which

provides information about ancient organisms


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Systematics is an analytical approach tounderstanding the diversity and relationships oforganisms, both present-day and extinct

Systematists use morphological, biochemical, andmolecular comparisons to infer evolutionaryrelationships


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Concept 25.1: Phylogenies are based on common ancestriesinferred from fossil, morphological, and molecular evidence

To infer phylogenies, systematists gatherinformation about morphologies, development,and biochemistry of living organisms

They also examine fossils to help establishrelationships between living organisms


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The Fossil Record

Sedimentary rocks are the richest source of fossils Sedimentary rocks are deposited into layers called

strata

Video: Grand Canyon
http://media/25_03GrandCanyon_SV.mpghttp://media/25_03GrandCanyon_SV.mpg


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LE 25-3

Rivers carry sediment to theocean. Sedimentary rock layerscontaining fossils form on theocean floor.

Over time, new strata aredeposited, containing fossilsfrom each time period.

As sea levels change and theseafloor is pushed upward,sedimentary rocks are exposed.Erosion reveals strata and fossils.

Younger stratumwith more recentfossils

Older stratum witholder fossils



The fossil record is based on the sequence inwhich fossils have accumulated in such strata

Fossils reveal ancestral characteristics that may

have been lost over time



Though sedimentary fossils are the most common,paleontologists study a wide variety of fossils

Animation: The Geologic Record
http://media/25_04GeologicRecord_A.htmlhttp://media/25_04GeologicRecord_A.html


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LE 25-4

Dinosaur bones beingexcavated from sandstone

Casts of ammonites, about375 million years old

Boy standing in a 150-million-year-old

dinosaur track in Colorado

Tusks of a 23,000-year-old mammoth, frozen whole

in Siberian ice

Petrified trees in Arizona, about 190million years old

Insects preserved whole in amber

Leaf fossil, about 40 millionyears ago



Morphological and Molecular Homologies

In addition to fossils, phylogenetic history can beinferred from morphological and molecularsimilarities in living organisms

Organisms with very similar morphologies orsimilar DNA sequences are likely to be moreclosely related than organisms with vastly differentstructures or sequences


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Analogous structures or molecular sequences thatevolved independently are also calledhomoplasies


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Evaluating Molecular Homologies

Systematists use computer programs andmathematical tools when analyzing comparableDNA segments from different organisms


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Concept 25.2: Phylogenetic systematics connectsclassification with evolutionary history

Taxonomy is the ordered division of organismsinto categories based on characteristics used toassess similarities and differences

In 1748, Carolus Linnaeus published a system oftaxonomy based on resemblances.

Two key features of his system remain useful

today: two-part names for species and hierarchicalclassification


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Binomial Nomenclature

The two-part scientific name of a species is calleda binomial

The first part of the name is the genus

The second part, called the specific epithet, isunique for each species within the genus

The first letter of the genus is capitalized, and theentire species name is latinized

Both parts together name the species ( not thespecific epithet alone)


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Hierarchical Classification

Linnaeus introduced a system for groupingspecies in increasingly broad categories

Animation: Classification Schemes

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http://media/25_08ClassSchemes_A.htmlhttp://media/25_08ClassSchemes_A.html


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LE 25-8

Species

Panthera pardus

Panthera Genus

FamilyFelidae

CarnivoraOrder

MammaliaClass

PhylumChordata

KingdomAnimalia

EukaryaDomain


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Linking Classification and Phylogeny

Systematists depict evolutionary relationships inbranching phylogenetic trees

LE 25-9


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LE 25 9

Carnivora

Panthera pardus

(leopard)

Mephitis mephitis

(striped skunk)

Lutra lutra (European

otter)

Canis familiaris

(domestic dog)

Canis lupus (wolf) S

p e c i e s

G e n u s

F a m

i l y

O r d e r

Felidae Mustelidae Canidae

Panthera Mephitis Lutra Canis


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Each branch point represents the divergence oftwo species

LE 25-UN497


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LE 25 UN497

Leopard Domestic cat

Common ancestor

Leopard Domestic catWolf

Common ancestor


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Deeper branch points represent progressivelygreater amounts of divergence


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A valid clade is monophyletic, signifying that itconsists of the ancestor species and all itsdescendants

LE 25-10a


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Grouping 1

Monophyletic


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A paraphyletic grouping consists of an ancestralspecies and some, but not all, of the descendants

LE 25-10b


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Paraphyletic

Grouping 2


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A polyphyletic grouping consists of variousspecies that lack a common ancestor

LE 25-10c


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Polyphyletic

Grouping 3

Sh d P i iti d Sh d D i d Ch t i ti


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Shared Primitive and Shared Derived Characteristics

In cladistic analysis, clades are defined by theirevolutionary novelties


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A shared primitive character is a character that isshared beyond the taxon we are trying to define

A shared derived character is an evolutionarynovelty unique to a particular clade

Outgroups


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Outgroups

An outgroup is a species or group of species thatis closely related to the ingroup, the variousspecies being studied

Systematists compare each ingroup species withthe outgroup to differentiate between sharedderived and shared primitive characteristics


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LE 25-11TAXA


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Hair

Amniotic (shelled) egg

Four walking legs

Hinged jaws

Vertebral column(backbone)

Character table

C H A R A C T E R S

TAXA

L a n c e

l e t

( o u

t g r o u p

)

L a m p r e y

T u n a

S a

l a m a n

d e r

T u r t

l e

L e o p a r d

Turtle Leopard

Hair

Amniotic egg

Four walking legs

Hinged jaws

Vertebral column

Salamander

Tuna

Lamprey

Lancelet (outgroup)

Cladogram

Phylogenetic Trees and Timing


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Phylogenetic Trees and Timing

Any chronology represented by the branching of aphylogenetic tree is relative rather than absolute inrepresenting timing of divergences

Phylograms


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Phylograms

In a phylogram, the length of a branch in acladogram reflects the number of genetic changesthat have taken place in a particular DNA or RNAsequence in that lineage

LE 25-12


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Ultrametric Trees


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Ultrametric Trees

Branching in an ultrametric tree is the same as ina phylogram, but all branches traceable from thecommon ancestor to the present are equal length

LE 25-13


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C e n o

z o i c

M e s o z o

i c

P a

l e o z o

i c

6 5

. 5

2 5 1

5 4 2

N e o p r o

t e r o z o

i c

M i l l i o n s o

f

y e a r s a g o

Maximum Parsimony and Maximum Likelihood


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Maximum Parsimony and Maximum Likelihood

Systematists can never be sure of finding the besttree in a large data set

They narrow possibilities by applying theprinciples of maximum parsimony and maximumlikelihood


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The most parsimonious tree requires the fewestevolutionary events to have occurred in the formof shared derived characters

The principle of maximum likelihood states that,given certain rules about how DNA changes overtime, a tree can be found that reflects the mostlikely sequence of evolutionary events

LE 25-14Human Mushroom Tulip


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0 30%

0

p

40%

40%

Human

Mushroom

0Tulip

Percentage differences between sequences

Comparison of possible trees

15% 15% 20%

5% 5%10%

15%

25%

Tree 1: More likely Tree 2: Less likely


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In considering possible phylogenies for a group ofspecies, systematists compare molecular data forthe species.

The most efficient way to study hypotheses is toconsider the most parsimonious hypothesis, theone requiring the fewest evolutionary events(molecular changes)

LE 25-15ab


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Sites in DNA sequence

I

Species

1

Base-changeevent

Bases atsite 1 foreach species

2 3 4 5 6 7

II

III

IV

I II III IV

Phylogenetic Trees as Hypotheses


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Phylogenetic Trees as Hypotheses

The best hypotheses for phylogenetic trees fit themost data: morphological, molecular, and fossil

Sometimes the best hypothesis is not the mostparsimonious

LE 25-16


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Lizard Bird Mammal

Four-chamberedheart

Mammal-bird clade

Lizard Bird Mammal

Four-chamberedheart

Four-chamberedheart

Lizard-bird clade

Concept 25.4: Much of an organisms


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Concept 25.4: Much of an organism sevolutionary history is documented in its genome

Comparing nucleic acids or other molecules toinfer relatedness is a valuable tool for tracingorganisms evolutionary history

Gene Duplications and Gene Families


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Gene Duplications and Gene Families

Gene duplication increases the number of genesin the genome, providing more opportunities forevolutionary changes


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Orthologous genes are genes found in a singlecopy in the genome

They can diverge only after speciation occurs

LE 25-17a


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Ancestral gene

Speciation

Orthologous genes


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LE 25-17b


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Ancestral gene

Gene duplication

Paralogous genes

Genome Evolution


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Orthologous genes are widespread and extendacross many widely varied species

The widespread consistency in total gene numberin organisms indicates genes in complexorganisms are very versatile and that each genecan perform many functions

Concept 25.5: Molecular clocks help track


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p pevolutionary time

To extend molecular phylogenies beyond thefossil record, we must make an assumption abouthow change occurs over time

Molecular Clocks


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The molecular clock is a yardstick for measuringabsolute time of evolutionary change based on theobservation that some genes and other regions ofgenomes seem to evolve at constant rates

Neutral Theory


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y

Neutral theory states that much evolutionarychange in genes and proteins has no effect onfitness and therefore is not influenced byDarwinian selection

It states that the rate of molecular change in thesegenes and proteins should be regular like a clock

Difficulties with Molecular Clocks


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The molecular clock does not run as smoothly asneutral theory predicts

Irregularities result from natural selection in whichsome DNA changes are favored over others

Estimates of evolutionary divergences older thanthe fossil record have a high degree of uncertainty

Applying a Molecular Clock: The Origin of HIV


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pp y g g

Phylogenetic analysis shows that HIV isdescended from viruses that infect chimpanzeesand other primates

Comparison of HIV samples throughout theepidemic shows that the virus evolved in a veryclocklike way

The Universal Tree of Life


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The tree of life is divided into three great cladescalled domains: Bacteria, Archaea, and Eukarya

The early history of these domains is not yet clear

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25. Sistematica Campbell